An existing high-speed turbine dental drill handpiece includes a handpiece head, a head cover, a drill pin, a front handle and a rear handle. See FIG. 1. The rear handle is connected to a quick-plug connector of a dental therapeutic machine for obtaining compressed air, pressurized cooling water, etc. required by the handpiece for working. The front handle is a portion held by a doctor. The handpiece head is internally equipped with a wind wheel which can be driven by compressed air. The wind wheel is supported by two bearings at the middle of the wind wheel shaft and is damped with two O-shaped rubber rings.
At present, such dental drill handpiece can generate a suckback phenomenon which may result in iatrogenic cross infection. The causes are below:
1) Generation of Contamination Sources
When using a high-speed turbine dental drill to drill teeth, a doctor must place the high-speed turbine dental drill in the oral cavity of a patient, and water is sprayed to cool the drill pin during the drilling, so the handpiece head and a part of the front handle of such handpiece inevitably touch the teeth, oral mucosa, dental pulp cavity, etc. of the patient, and sometimes the blood, and the cooling water sprayed to the drill pin during the treatment and the saliva of the patient generate contaminating liquid in the oval cavity of the patient. If the treated patient has some transmitted diseases, such as hepatitis B, Hepatitis C and AIDS, then such contaminating liquid inevitably contains a huge amount of harmful viruses and bacteria.
2) Iatrogenic Cross Infection Caused by Suckback
The existing high-speed dental drill handpiece generates the suckback phenomenon when drilling teeth, which is known in the field.
As shown in FIG. 2 and FIG. 3, when the compressed air enters the handpiece head via the air inlet and blows the wind wheel to rotate, the wind wheel chamber is in a positive pressure state. In such circumstances, suckback is not generated. When a doctor is going to stop the handpiece from rotating, the compressed air flow disappears via the air inlet of the head 1, and the wind wheel continues to rotate for a period of time by inertia. Due to no supply of the compressed air in the air inlet, the rotating wind wheel sucks air from seams at the upper and lower ends of the head and exhausts the air into the air inlet and the exhaust opening. In such circumstances, at this place, the handpiece head easily sucks the above mentioned oral contaminating liquid or atomized contaminating liquid drops suspended in the oral cavity or fine particles ground off from the teeth into the wind wheel cavity thereof and exhausts the sucked substances into the exhaust opening, thus contaminating components (such as the wind wheel, bearing, etc.) in the cavity of the head and the air exhaust tube, and even transmitting the sucked substances into the pipelines and related components of the therapeutic machine. When the doctor treats the next patient, such contaminants adhered to the interior of the cavity of the handpiece head of the turbine dental drill handpiece and to the pipes and components of the therapeutic machine are sprayed into the oral cavity of the next patient along with the compressed air, thus generating iatrogenic cross infection.
In the prior art, the technical material with the proximate technical characteristic is patent ZL20061020074.X which is entitled “Suckback Prevention Device for Disposable High-Speed Turbine Dental Drill Handpiece”. FIG. 4 is a drawing of the patent in 2006.
The prior art mostly focuses on the suckback prevention device disposed on one side of the handpiece where the drill pin is installed and effective prevention of the negative pressure suckback phenomenon generated due to the inertia rotation of the wind wheel after the supply of the compressed air is stopped. Even in a water immersion test, no substance is sucked when one side of the handpiece is immersed in water (the side of the head equipped with the drill pin is immersed in water after rotating; after the handpiece stops rotating in water, take out the handpiece and weight it, wherein the difference of the weight before and after the water immersion is the suckback quantity). See FIG. 5 and FIG. 9. However, considerable sucked substances flow into the turbine cavity in the fully immersed state (the whole handpiece head is immersed in water). See FIG. 5 and FIG. 10.
For the existing patent ZL20061020074.X, the elastic shaft sealing casing thereof can complete sealing and braking at the moment when the air supply to the wind wheel is stopped. Due to the sealing effect, the handpiece immersed in the water can prevent water (contaminants) from being sucked into the wind wheel chamber. Therefore, no water can enter the turbine cavity and no substance is sucked back. However, it should be noted that the wind wheel cavity is still in the negative pressure state in such moment and needs to be supplemented with the external air to keep balance with the atmospheric pressure. Therefore, a relatively large clearance exists between the button housing and the head housing on one side of the head cover. Naturally, the air is supplemented via the clearance to keep balance with the external atmospheric pressure. In such circumstances, if the handpiece head is completely immersed in water, water enters the turbine cavity via the clearance between the head housing and the button housing by the negative pressure effect of the wind wheel chamber, resulting in iatrogenic cross infection.
The above water immersion test represents that the patent ZL20061020074.X and other suckback prevention devices disposed only on one side have the suckback prevention function and can even achieve zero-suckback in the one-side water immersion test, but fail to stop the suckback when the handpiece head is fully immersed in water; in the full water immersion test, the sucked substances enter the wind wheel chamber from the other side, so the suckback phenomenon still exists and the iatrogenic cross infection may exist. See FIG. 5 and FIG. 6.
Experiments show that the handpiece which achieves the zero suckback when immersed in the water on one side (the side where the handpiece head is equipped with the drill pin) still sucks dozens or hundreds of milligrams of substances in the full water immersion test.